PBES Seismic Research at the University of Washington

John Stanton, Marc Eberhard, Kyle Steuck , Jason Pang, Todd Janes,

Olafur Haraldsson, Hung Viet Tran, Phillip Davis, Gunnsteinn Finnsson, Jeffrey Schaefer.

University of Washington

FHWA P2P Exchange Workshop,Seattle, 2011.11.15

Partners

• WSDOT

• Berger-ABAM

• Concrete Technology Corporation

• Tri-state Construction

Acknowledgments• FHWA (Highways for Life)

• WSDOT

• PEER

• TransNOW

• Valle Foundation

• PacTrans

• NSF-NEES

ObjectiveDevelop a family of seismic bridge PBES connections for:

• Rapid construction

• Superior seismic performance

Designers can mix and match connections to suit local conditions.

Key Elements1. Large bars grouted in ducts. (Rapid construction)

Key Elements

2. Socket connections. (Rapid construction)

Key Elements3. Unbonded pre-tensioned columns. (Seismic performance)

Construction Procedure

1) Excavate footing.

2) Position and brace precast column.

Construction Procedure

3) Place footing reinforcement and cast.

Construction Procedure

4) Set cap-beam, grout bars into ducts.

Construction Procedure

5) Place girders, diaphragms and deck.

Construction Procedure

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

Large Bar Connection (Cap Beam)

• Bars grouted into ducts.

• Few, large bars simplify fit-up.

• Is development length a problem?

Large Bar Connection (Cap Beam) #18 Bar Anchorage Tests

- Pullout tests.

- Need 6db to develop yield, 10db to develop fracture.

- Bar can easily be anchored within cap beam.

Large-Bar Connection

Cyclic Lateral Load Testing

Large-Bar Connection

• Failure occurs in the column.

• PC Connection behaves the same as c.i.p.

Cyclic Lateral Load Testing

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

Footing Connection: Construction

Headed bars

Footing Connection - PerformanceHeaded bars provide good load transfer.

Internal forces:

Strut and Tie Model.

Footing ConnectionHooked bars facing out(Conventional cip)

Load transfer is tangential to hook.

Poor transfer.

Spread Footing Connection

Vertical (gravity) load.

Lateral (seismic) load.

Spread Footing ConnectionConstructability:

• Column has no projecting bars.

• No “form-savers”.

• Easy to fabricate and transport.

Note: Top steel not yet in place

Spread Footing Connection

Structural Performance• Terminators provide better anchorage than

hooked bars facing outwards.• Failure occurs in column, not footing. • Seismic performance as good as, or better

than, conventional c.i.p. construction.

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

Drilled-Shaft Connection

Drilled-Shaft Connection

DS-1 DS-2

Drilled-Shaft Connection

Performance depends on spiral in transition region.• 100% c.i.p. spiral failure in column.• 50% c.i.p. spiral failure in transition.

Hoop tension strength of transition region concrete appears to be important.• Third drilled shaft specimen (in lab now)

has thin concrete in transition region.

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

Background

Unbonded prestressing tendons for elastic restoring force.

Yielding steel for energy dissipation.

Self-centering structural systems

Pre-Tensioned System

1.Pre-tensioning solves corrosion problems perceived to exist in post-tensioning.

2.Pre-tension in a plant.

• Good QC.

• No special equipment or extra site time needed (compare with post-tensioning).

3. Can add rebars for energy dissipation.

Pre-Tensioned System PC cap-

beamSleeved strand

Bonded strandc.i.p.

footing

Bonded rebar

Cracking plane

Test Specimens

Footing specimen

Cap beam specimen

Test Specimens- Footing

connection

Test Specimens- Footing details

Screw-thread adjustment deviceLoad cell

Strand chuck

Strand sleeve

Bonded region

Void under column

2% drift

Load vs. Displacement

-15 -10 -5 0 5 10 15-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Drift [%]

Mom

ent

[kip

-in.]

RC: does not re-center

-15 -10 -5 0 5 10 15-3000

-2000

-1000

0

1000

2000

3000

Drift [%]

Mom

ent

[kip

-in.]

UBPT: re-centers

Preliminary Results

1. System re-centers.

2. No strands broke.

3. No loss of strand bond.

5. Damage to concrete at interface, possibly promoted by stub bars from footing.

New pre-tensioned specimen in lab now:

1.Use HyFRC (Hybrid fiber reinforced concrete) in the plastic hinge zone to reduce crushing.

2.Use stainless steel rebars to increase drift capacity and energy dissipation.

Thank You

Background

Accelerate on-site bridge construction.

Use precast concrete components.

Connection details:

seismic-resistant

construct

Column-to-Cap-BeamConnection

Precast column

Precast cap beam

6 # 18 rebar

8.5” corrugated steel ducts

High strength grout

Cap-Beam Connection: Large bars

Column-to-FootingConnection

Pre-Tensioned System

2% drift

6% drift

Spread Footing Connectionafter seismic testing

Foundation undamaged.

Spread Footing Connection – Gravity Load Test

(Damaged) column crushed at: 3.5 * (1.25DL + 1.75LL).

No damage to footing. No sign of punching failure.

-15 -10 -5 0 5 10 15-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Drift [%]

Mom

ent

[kip

-in.]

-15 -10 -5 0 5 10 15-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Drift [%]

Mom

ent

[kip

-in.]

SF-1

• Hf/Dc = 1• Slots in column base• More diagonal rft.• 100% Caltrans

stirrups

SF-2 • Hf/Dc = 1• No slots• Less diagonal rft.• 50% Caltrans stirrups

Spread Footing Thickness

SF-1 and SF-2.

Hfoot = Dcol

SF-3.

Hfoot = 0.5 Dcol

-15 -10 -5 0 5 10 15-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Drift [%]

Mom

ent

[kip

-in.]

SF-1

• Hf/Dc = 1.0• Slots in column base• More diagonal rft.• 100% Caltrans stirrups

SF-3 • Hf/Dc = 0.5• No slots• Less diagonal rft.• Heavy beam shear

reinforcement

-15 -10 -5 0 5 10 15-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Drift [%]

Mom

ent

[kip

-in.]

SF Movie

After testing.

SF-3

Fir

st "

sig

nifi

can

t" h

ori

zon

tal c

rack

Fir

st "

sig

nifi

can

t" d

iag

on

al c

rack

Fir

st r

esi

du

al o

pe

n c

rack

Fir

st y

ield

of l

on

g. r

ein

forc

em

en

t

Fir

st s

pa

llin

g

Fir

st s

pa

llin

g in

foo

ting

"Sig

nifi

can

t" s

pa

llin

g

Fu

lly s

pa

lled

Lo

ng

. ste

el e

xpo

sed

Ba

r b

uck

ling

Fir

st s

pir

al f

ract

ure

Fir

st b

ar

fra

ctu

re

0

2

4

6

8

10

12

SF-1 SF-2 SF-3

Dri

ft R

atio

(%

)

DS-1

• 100% transverse reinforcement in transition region

DS-2 • 50% transverse

reinforcement in transition region

Next Steps:

1.Test pretensioned, cap-beam specimen.

2. Bond tests on epoxy-coated strand.

3. Data analysis and design methodologies.

Looking Forward:

4. Methodology calibration tests (Grouted ducts, spread footings, drilled shafts)

5. High-performance materials (e.g. ECC at rocking interface).

Precast

prestressed

c.i.p.

RC (ref)

Precast

RC

Cap-beam

to column

Column to

spread footing

Column to

drilled shaft

Connection

Details

NEXT !